Hello all,

According to this site (http://www.paperlined.org/dev/oss/high_energy_slings/), KE of projectile is equal to 1/2 L Fc, where L is sling length and Fc is centripetal force.

Fc is linked to the force of the thrower (F) but I have not found any source that explains how to deduce Fc from F. Obviously there are some losses (weight of the sling for example and maybe also some part of the arm).

For throwing a javeling for example, there are some papers on the Web that demonstrates that Ec = L x 1/(1 + mw/m) Fn, where m is the mass of the javelin and mw a virtual mass to account for losses (the hand and some part of the arm). This virtual mass for a standard human is about 600 g.

I suppose this should be simlar for the sling, but I have found nothing on the Web. Any idea?

You cannot work out any useful information by calculating the centrifugal force unless the sling is very long so that the trajectory of the projectile before release is nearly circular.

So what do you want to find out by measuring the centrifugal force  ? Maybe there is a better way to do it.

There is just one force here, the thrower exerts on the cord which exerts on the stone. In the case of the stone satisfying circular motion it is the centripetal force.

The problem is for the throwing motion the circular motion model will likely not apply without at least some modification.

The tension is a function of the mass and the angular velocity but who cares unless you can actually measure the tension?  It seems easier to use 1/2m*v^2 and measure the velocity of a known projectile.

NooneOfConsequence wrote on Jun 21^st, 2019 at 12:58am:

The tension is a function of the mass and the angular velocity but who cares unless you can actually measure the tension?  It seems easier to use 1/2m*v^2 and measure the velocity of a known projectile.

Indeed, but imagine you only know the strength of the thrower (Fn) and the characteristics of both the sling (L, ms) and the projectile (mw). There should be a way to figure out how much of L x Fn is converted into kinetic energy.

Or the reverse. That is, if you know KE (by measurement for example) can you deduce the strength of the thrower?

Obviously there is some loss due to the weight of the sling and maybe, depending on the speed of rotation, some drag force applied to the string. But the Web is quite mute on that topic, contrary for example to javelin throwing, in which the efficiency factor is given by 1/(1+M/mw), where M is a virtual mass, roughly equal to 1/3 of 2.5% of the body mass (≈ hand and forearm mass).

I think you are confused or I misunderstand something.

iron wrote on Jun 25^th, 2019 at 2:57pm:

Indeed, but imagine you only know the strength of the thrower (Fn) and the characteristics of both the sling (L, ms) and the projectile (mw). There should be a way to figure out how much of L x Fn is converted into kinetic energy.

How do you measure the strength of the thrower in such a complex and dynamic movement ?
L of sling and the L in W=L*Fn is not the same also it's a vector dot product not just a multiplication of numbers, what it means is that any force perpendicular to motion is not contributing as work, so centrifugal force has nothing to do with work, only that it redirects the projectile, also the trajectory of the projectile during the throw is not straight in any way, the radius which you need to use in the centrifugal force formula is constantly changing.

for the formula to be used you need stupid long slings.Or measure the radius and force just when you release which would be much easier if you measured the "muzzle" velocity with a camera.The formula can work on what comes once you accelerate

to accelerate a projectile into a "perfect" circular motion, the pull on the sling must first be off center of the circle and at that moment is when you put energy into the system .and any more energy you put in the same manner once in circular motion is to fill energy losses

the best way to measure the efficiency of slinging is use a 3D tracker and track every movement of the joints and body so you can somehow know(if you can find the mass of every joint) how much energy you put to move yourself and the projectile , at the same time you measure the "muzzle" speed of the projectile which is your output energy and then divide the two and you got efficiency.

I went to an archery site KE calculator.... 250gr stone at 40m/s,  120 joules!  about a .22 cal

correction, 200g at 120fps...  96 joules, 1.6momentum :o

1/2 pound at 40m/s = 129 joules of KE & 1.9 momentum kg*m/s        its the latter they call "slug" .   slug is what drops carbon life forms. :-?

Banshee wrote on Sep 30^th, 2019 at 7:37pm:

1/2 pound at 40m/s = 129 joules of KE & 1.9 momentum kg*m/s

  that's a 9.04 kg*m/s

you would need a bowling ball at 30 mph to generate a slug of 9. The math is clear, 40m=131ft, 227g=.5lb. , 1gram=~15grains,       the archery KE calculator uses grains, maybe the source of confusion.  I use a 160g, 2400grain lacrosse ball at ~40m/s producing ~100 joules KE with a slug ~1.3 ::)

what is a "slug 1.3"?

momentum= velocity x mass (S.I.)

9.04 kg*m/s= 40m/s  x 0.226kg

1/2 pound= 0.226kg

use  0.1kg for 100g, or 1500gr

@ Banshee
you should stick to one system of measurement, or you'll get everyone confused.
g = grams
gr = grains

what is "slug ~ 1.3 " in S.I. ?

...so the force of the caster is difficult to measure , but easy to extrapolate!   the whitetail archery KE calculator tells us the "muzzle" KE of the projectile at 131fps, theaverage velocity of a caster. also known as    40m/s.     Slug is a ballistic term for "stopping force".      think of the diffence between getting hit with a railroad spike at 40mph, or nutrino at lightspeed(like right now!). the math is the same. :o